1. Field of the Invention
The present invention relates to a communication path calculation method and module. More particularly, the present invention relates to a communication path calculation method and a module that are implemented or incorporated in a transmission apparatus (hereinafter referred to as a node) including a reconfigurable optical add/drop multiplexer (ROADM) which performs wavelength division multiplex (WDM), advertises information on a wavelength which can be added or dropped, as information on a link, and autonomously calculates a communication path on the basis of the information.
2. Description of the Related Art
In recent years, the generalized multi-protocol label switching (GMPLS) method has come into the spotlight as a novel technology for supporting a new-generation super-high-speed backbone, and it will soon be put to practical use. GMPLS is an extension of MPLS, which has been adapted to an IP virtual private network (VPN), and is intended to allow MPLS to be employed in an optical network. A label switching technique of assigning a label to a packet and switching paths on the basis of the label information can be used to transmit a light signal with respect to each wavelength. This permits high-speed switching with the light signal left intact. Moreover, GMPLS has high affinity with prior arts, because it can manage and control IP-based data communication, and has the advantage of allowing construction of a high-speed network that is highly scalable.
Conventionally, when a signaling protocol is used to dispersively determine a path, a GMPLS control plane calculates a path on the basis of information on a topology that is exchanged according to a routing protocol such as an open shortest path first-traffic engineering (OSPF-TE) routing protocol developed by the Internet engineering task-force. The information on the path is used to determine an end-to-end path in the process of signaling based on the resource reservation protocol-traffic engineering (RSVP-TE). At this time, a label indicating the path, (which represents a time slot in the case of the synchronous optical network (SONET) system adopting the synchronous digital hierarchy (SDH), or represents a wavelength in the case of a wavelength-division multiplexed (WDM) network), is assigned to a packet.
FIG. 1 shows an example of a WDM ring network having communication nodes in a ring configuration. FIG. 2 shows an example of the configuration of a communication node. FIG. 3 shows an example of the concrete configuration of a switch unit (SW) shown in FIG. 2.
In FIG. 1, the WDM network has nodes 1 to 4, each of which includes a ROADM module, interconnected in a ring configuration. The drawing indicates wavelengths λ1 to λ10 accommodated by the WDM ring network and wavelengths which a transponder incorporated in each of the nodes 1 to 4 can add or drop (for example, the node 1 can add or drop wavelengths λ1 to λ4 and λ7 to λ10). Ring Flag:ON in the drawing signifies, as described later in conjunction with FIG. 4B and FIG. 4C, that the nodes are interconnected in a ring configuration.
FIG. 2 shows an example of the configuration of each of the nodes 1 to 4 including a ROADM module or the like.
Typical transmission equipment includes an intra-equipment monitoring control unit 21 that manages and controls the equipment and that includes an equipment manager 22, which manages the equipment, and an alarm monitor 24, that monitors a transmission channel to detect a failure or the like. In this example, that includes the GMPLS control plane, the intra-equipment monitoring control unit 21 also includes a GMPLS controller 23 that controls a signaling facility. The present invention relates to the equipment manager 22 and GMPLS controller 23.
FIG. 3 shows an example of a concrete configuration including a switch unit 25 and interfaces 26 and 27 that are characteristic of the ROADM module.
The interfaces 26 or 27 are realized with wavelength multiplexers 26 each of which separates a WDM signal λ1-10, which is a bundle of signals of different wavelengths (ten wavelengths in this example), into individual signals of different wavelengths, or wavelength demultiplexers 27 each of which combines the signals of different wavelengths so as to restore the original WDM signal λ1-10. An optical amplifier that is not shown may be incorporated in each of the wavelength multiplexers 26 or wavelength demultiplexers 27.
The switch unit (SW) 25 includes switches 33 and 34 which are connected to WDM links 10 and 21 respectively that deal with the WDM signal λ1-10, so that the node can be reconfigured. The switch 33 selects whether a signal 2 that has a certain wavelength and is one of signals resulting from multiplexing should be added or dropped or passed through a transponder 1 (IF1). The switch 34 selects whether a signal 10 that has a certain wavelength and is one of the signals resulting from multiplexing should be added or dropped or passed through a transponder 2 (IF2).
Moreover, publicly-known literature has disclosed that wavelength-division multiplexing (WDM) transmission equipment notifies a SONET/SDH system of the identifier of an interface and a wavelength to be passed through the interface and that, if a failure occurs, the SONET system notifies the WDM equipment of the wavelength (refer to Patent Document 1).
Patent Document 1: Japanese Unexamined Patent Publication No. 2004-522691
However, as far as reconfigurable optical add/drop multiplexers (ROADMs) interconnected over a WDM network are concerned, the wavelength each ROADM can add or drop is determined on a fixed basis according to a physical line led to an input/output port of a transponder or the like included in each node. Conventionally, the information on the wavelength has not been advertised using the OSPF routing protocol or the like. Therefore, a path cannot be automatically calculated. This poses a problem in that maintenance and operation personnel have to manually enter information on restrictions to be imposed on routing.
According to the conventional GMPLS method (OSPF-TE routing protocol), a switch included in equipment is supposed to work in a non-blocking manner. No consideration is taken into a blocking ability inherent to transmission equipment including a ROADM or the like. A path cannot be calculated using information on a network acquired using the OSPF-TE routing protocol. In efforts to solve this problem, a link at which restrictions are imposed is manually designated or a network management system is used to calculate a path. This is time-consuming.
Moreover, in the aforesaid first example, information on a wavelength and information on an interface are provided. In the present application, pieces of information on intra-equipment connections are also provided. Moreover, in the aforesaid first example, information is exchanged between adjoining pieces of equipment. In the present application, information is exchanged within an entire ring or network.